The application of an exhaust heat exchanger to protect the catalyst and improve the fuel economy in a spark-ignition engine

Abstract

A close-coupled catalyst (CCC) can reduce engine cold-start emissions by utilizing the energy in the exhaust gas. However, in case the engine is operated at high engine speed and load condition, the catalytic converter may be damaged and eventually deactivated by thermal ageing. Excess fuel is sometimes supplied intentionally to lower the exhaust gas temperature, avoiding thermal ageing. This sacrifices fuel economy and exhaust emissions. This paper describes the results of an exhaust heat exchanger to lower the exhaust gas temperature, mainly under high load conditions. The heat exchanger was installed between the exhaust manifold and the inlet of the CCC to avoid thermal ageing. The exhaust heat exchanger successfully decreased the exhaust gas temperature, which eliminated the requirement of fuel enrichment under high-load conditions. A reduction of fuel consumption by approximately 7.7 per cent at high vehicle speed was achieved due to no fuel enrichment. Although the amount of hydrocarbon during the cold start increases due to the increment of the catalyst light-off time, it still meets the EURO-IV regulations. This problem could be resolved by adopting the solenoid valve to cut off the coolant at the inlet of the coolant passage of the heat exchanger.